The purpose of this shared instrumentation grant is to obtain funds for the purchase of a JEOL JEM 1200 TEMSCAN analytical electron microscope. This microscope will be housed within the electron microscope laboratory of the Department of virology and Immunology at Southwest Foundation for Biomedical Research, which currently contains two transmission electron microscopes: an AEI EM6B which was purchased in 1966 and an Hitachi HU 11C which was obtained in 1967. These microscopes are the only ones available for use at SFBR. Both are over 20 years old and are frequently unavailable because of disrepair. More important, neither instrument has scanning capability, therefore scanning EM technology is not available at the Foundation. Replacement part for both instruments are becoming increasingly difficult to obtain. In addition, these microscopes lack the ease of operation, simplicity of alignment procedures, and automation of the vacuum and camera systems which save a significant amount of operator time and make the JEOL 1200 EX TEMSCAN particularly well suited to the needs of a multi-user facility. The 1200 EX TEMSCAN also has several important features not available in the older microscopes, including a focusing aid for use at low magnification, a eucentric goniometer stage to allow tilting of the specimen, a high-contrast objective lens, and an extremely high vacuum in the specimen chamber to reduce contamination of samples. This electron microscope is being requested to physically replace both microscopes. The major users group consists of Drs. R.E. Lanford, D.L. Bronson, P. Kanda, J.S. Allan, H.C. McGill, Jr., R.S. Kushwaha, J. Eichberg, G.B. Hubbard, T.M. Butler, R.C. Kennedy, R.A. deLemos, J.A. Coalson, and G.R. Dreesman. All members of the users group use or expect to use electron microscopy as a primary tool in their individual NIH-funded research projects. The age and condition of the existing microscopes cause significant delays and reduced quality of results in these research efforts. The acquisition of a JEOL 1200EX TEMSCAN will provide a modern, reliable, high- resolution instrument needed to carry out both transmission and scanning electron-microscopy-related research of the major users groups and will provide electron microscopy service to these investigators and to other members of SFBR.